Rapid cabin heating of a motor vehicle is desired, particularly during cold ambient conditions, to provide passenger comfort. Classically, cabin heat comes from the engine coolant, which may be heated indirectly via a massive increase in exhaust heat. However, such a method is energy inefficient and wastes fuel, as only a small fraction of the exhaust heat appears in the engine coolant.
The inventors have recognized that exhaust heat whose route is altered by throttling the exhaust may be recovered and directly routed to the cabin heating system rather than indirectly routed to the cabin heating system via the engine coolant system. Further, the inventors have also recognized that by varying the flow rate of coolant into the cabin heating system as the characteristics of the system (e.g., coolant temperature, blower fan speed, etc.) change, an optimal amount of heat may be transferred from the exhaust to the cabin heating system. Accordingly, a method for an engine is provided, comprising pumping coolant from a coolant reservoir to an exhaust component and then to a heater core, the coolant heated by the exhaust component, and during engine warm-up conditions, adjusting a flow rate of coolant into a heater core to maximize heat transfer to a vehicle cabin.
In one example, the coolant is sourced from the engine's general coolant system, passes through a heat pick up element (e.g., EGR cooler) and then passes through a heat sink (the heater core), and is released into the engine's general coolant system. During non-steady state conditions, such as when the engine is heating up, there is a coolant flow rate (that is not necessarily the maximum flow rate) that achieves maximum heat transfer into the heater core. That coolant flow rate is a function of the heater core temperature drop (ΔT). The maximum heat is transferred when the product of ΔT and flow rate are maximized. However, during steady state conditions, such as when the engine has reached operating temperature, the coolant may be flowed at a constant flow rate, such as maximum flow rate. In this way, as the system characteristics change during engine warm-up, the flow rate may be continually adjusted to maintain maximum heat transfer to the cabin and thus promoting efficient cabin heating.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.